git.distorted.org.uk Git - u/mdw/catacomb/blob - calc/ecp.cal

   1 /* -*-apcalc-*-
   2  *
   3  * $Id: ecp.cal,v 1.1 2000/10/08 16:01:37 mdw Exp $
   4  *
   5  * Testbed for elliptic curve arithmetic over prime fields
   6  *
   7  * (c) 2000 Straylight/Edgeware
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of Catacomb.
  13  *
  14  * Catacomb is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU Library General Public License as
  16  * published by the Free Software Foundation; either version 2 of the
  17  * License, or (at your option) any later version.
  18  *
  19  * Catacomb is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU Library General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU Library General Public
  25  * License along with Catacomb; if not, write to the Free
  26  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  27  * MA 02111-1307, USA.
  28  */
  29
  30 /*----- Revision history --------------------------------------------------*
  31  *
  32  * $Log: ecp.cal,v $
  33  * Revision 1.1  2000/10/08 16:01:37  mdw
  34  * Prototypes of various bits of code.
  35  *
  36  */
  37
  38 /*----- Object types ------------------------------------------------------*/
  39
  40 obj ecp_curve { a, b, p };
  41 obj ecp_pt { x, y, e };
  42
  43 /*----- Main code ---------------------------------------------------------*/
  44
  45 define ecp_curve(a, b, p)
  46 {
  47   local obj ecp_curve e;
  48   e.a = a;
  49   e.b = b;
  50   e.p = p;
  51   return (e);
  52 }
  53
  54 define ecp_pt(x, y, e)
  55 {
  56   local obj ecp_pt p;
  57   p.x = x % e.p;
  58   p.y = y % e.p;
  59   p.e = e;
  60   return (p);
  61 }
  62
  63 define ecp_pt_print(a)
  64 {
  65   print "(" : a.x : ", " : a.y : ")" :;
  66 }
  67
  68 define ecp_pt_add(a, b)
  69 {
  70   local e, alpha;
  71   local obj ecp_pt d;
  72
  73   if (a == 0)
  74     d = b;
  75   else if (b == 0)
  76     d = a;
  77   else if (!istype(a, b))
  78     quit "bad type arguments to ecp_pt_add";
  79   else if (a.e != b.e)
  80     quit "points from different curves in ecp_pt_add";
  81   else {
  82     e = a.e;
  83     if (a.x == b.x) {
  84       if (a.y != b.y) {
  85         return (0);
  86       }
  87       alpha = (3 * a.x^2 + e.a) * minv(2 * a.y, e.p) % e.p;
  88     } else
  89       alpha = (b.y - a.y) * minv(b.x - a.x, e.p) % e.p;
  90
  91     d.x = (alpha^2 - a.x - b.x) % e.p;
  92     d.y = (-a.y + alpha * (a.x - d.x)) % e.p;
  93     d.e = e;
  94   }
  95
  96   return (d);
  97 }
  98
  99 define ecp_pt_neg(a)
 100 {
 101   local obj ecp_pt d;
 102   d.x = a.x;
 103   d.y = -a.y;
 104   d.e = a.e;
 105   return (d);
 106 }
 107
 108 define ecp_pt_mul(a, b)
 109 {
 110   local p, n;
 111   local d;
 112
 113   if (istype(a, 1)) {
 114     n = a;
 115     p = b;
 116   } else if (istype(b, 1)) {
 117     n = b;
 118     p = a;
 119   } else
 120     return (newerror("bad arguments to ecp_pt_mul"));
 121
 122   d = 0;
 123   while (n) {
 124     if (n & 1)
 125       d += p;
 126     n >>= 1;
 127     p += p;
 128   }
 129   return (d);
 130 }
 131
 132 /*----- That's all, folks -------------------------------------------------*/
 133